1. Field of the Invention
This invention relates generally to self-tuning pianos and, more particularly, to a piano string tuning apparatus that tunes piano strings by inducing an alternating current in the piano string through mutual inductance.
2. Related Art
U.S. Pat. No. 6,559,369 to Gilmore (“Gilmore”) entitled “Apparatus and Method for Self-Tuning a Piano,” filed on Jan. 14, 2002, which is now U.S. Pat. No. 6,559,369, the entire disclosure of which is hereby incorporated by reference in its entirety, describes a self-tuning piano that tunes piano strings by passing electrical current through the metal piano strings, thereby causing the piano strings to increase in temperature. Such an increase in temperature causes the piano strings to thermally expand and elongate, thereby lowering the tension and pitch of the piano string. By varying an electrical current in the piano string, a supervisory circuit can accurately control the pitch of the piano string until the piano string is in tune.
While some notes of a piano comprise only one piano string, some notes of the piano are grouped into sets of two or three piano strings, tuned in unison. All piano strings pass through an agraffe. An agraffe is a brass stud with one, two, or three holes, depending on the number of piano strings comprising a particular note. Because brass is a conductive material, as many as three piano strings are electrically connected through the agraffe. Because multiple piano strings are electrically connected through one agraffe, controlling the current for an individual piano string is impossible. As a solution, Gilmore proposed agraffes constructed using an electrically-insulating material so that electrical current may be applied to each piano string individually.
The electrically-insulated agraffe solution invented by Gilmore required insulating agraffes to be installed in a new piano at the factory, or, for existing pianos, the solution invented by Gilmore required complete replacement of all electrically-conductive agraffes within the piano with electrically-insulating agraffes. Complete agraffe replacement is a time-consuming, tedious, and costly operation because the piano must be restrung after replacement of the agraffes. Another disadvantage of the electrically-insulated agraffe is that the insulating material may affect the tone and timbre of the piano adversely, or cause the agraffe to be too weak to handle the high tensile forces of the piano strings.